EP2092368B1 - Method and device for detecting precipitation using radar - Google Patents

Abstract

A method for detecting precipitation in a region monitored by radar beams includes ascertaining a first average power of a first backscattered radar signal, ascertaining a second average power of a second backscattered radar signal, and detecting an existence of a homogenous medium when the average powers conform.

Description

The invention relates to a method for detecting precipitation in a radar-detected area according to claim 1, an apparatus for carrying out this method, a computer program and a computer program product.

State of the art

Precipitation, such as rain, hail, fog or snowfall, can be detected by radar. For example, in meteorology, the precipitation intensity can be determined by means of radar, in that a directional antenna radiates pulse-shaped electromagnetic radiation in the microwave range. For this purpose, a radar system can be used that emits radar beams with a wavelength of about 3 to 10 cm. If the radiation in the atmosphere hits a particle whose diameter is greater than about 0.2 mm, the radiation is reflected by it. The wavelength of the radiation does not change. Part of this radiation is picked up by a receiver of the radar and the reflectivity is measured. From the reflectivity, the precipitation intensity can be calculated if certain assumptions are made about the particle or droplet size distribution of the precipitate. A conversion then takes place with a so-called Z-R relationship, where Z stands for reflectivity and R for the precipitation intensity.

The WO 1993002370 A1 describes a method for detecting rain. Several radar signals are emitted. Backscattered signals are received, to create a Doppler spectrum. A reduced amplitude in the Doppler spectrum, especially in the peripheral regions of the spectrum, indicates rainfall.

The EP 1229348 A1 describes a system for detecting rain or hail by means of a weather radar. Different standard deviation and return radiation intensity maps are combined with each other.

The JP 07248830 A describes a device for correcting a calculated rainfall intensity in the context of a radar.

The JP 10048333 A describes a radar with which snowfall or rain can be detected by receiving a reflected signal and measuring its level.

A method for detecting precipitation by means of two radar beams for aircraft is known from US 5,028,929 known. In this case, at least two radar signals are transmitted, wherein the sizes of backscattered radar signals are determined. A determination of the presence of precipitation is made by comparing the thus determined attenuation characteristics of the two backscattered radar signals.

A similar prior art is from the document SENBOKUYA Y ET AL: "Development of the spaceborne dual frequency precipitation radar for the global precipitation measurement mission" GEOSCIENCE AND REMOTE SENSING SYMPOSIUM; 2004. IGARSS # 04. PROCEEDINGS. 2004 IEEE INTERNATIONAL ANCHORAGE, AK, USA 20-24 SEPT. 2004, PISCATAWAY, NJ, USA, IEEE, Vol. 5,20. September 2004, pages 3570-3573, XP010750760, ISBN: 0-7803-8742-2 " known.

Disclosure of the invention

Against this background, the present invention proposes a method for detecting precipitation in a region covered by radar beams, furthermore a device which uses this method, and finally a corresponding computer program and a computer program product according to the independent patent claims. Advantageous embodiments emerge from the respective subclaims and the following description.

In the method according to the invention for detecting precipitation in a region detected by radar beams, a first average power of a first backscattered radar signal and a second average power of a second backscattered radar signal are determined. According to the invention, a presence of precipitate is determined by a comparison of the mean powers with each other

A determination of the correspondence of the average powers takes place according to the invention taking into account at least one weighting factor, wherein the at least one weighting factor is designed to compensate for different radar antenna characteristics. By using weighting factors, the average powers can be compared even if the underlying radar signals originate from differently designed radar transmitters. This increases the flexibility of the method according to the invention.

In a preferred embodiment, a correspondence of the mean powers is determined by means of correlation of the respectively determined average powers.

In an advantageous embodiment of the method according to the invention, a determination of a further average power of a further backscattered radar signal takes place.

The evaluation of more than two backscattered radar signals increases the accuracy of the detection of precipitation. The backscattered radar signals may be reflections of radar signals emitted by adjacent radar transmitters.

According to a preferred embodiment, the mean powers are determined in each case for an object-free section of the detected area.

According to one embodiment, in order to determine the average powers, in each case a spectral power density for each backscattered radar signal is detected and superimposed on the object-free section.

According to a preferred embodiment of the method according to the invention, the object-free section can be determined by an analysis of the spectral power densities of the backscattered radar signals. In this case, the object-free section corresponds to a common subarea of the spectral power densities in which none of the spectral power densities has a peak that protrudes above a noise floor of the respective spectral power density.

According to a further preferred embodiment, a density of the precipitate or a radar signal attenuation can be determined. This can be done by evaluating an increase in the noise floor of at least one of the spectral power densities.

The precipitation can be, for example, rain, snow, fog or hail. A main direction of movement of the precipitate may be orthogonal to the Be radar beams. Advantageously, the precipitate according to the inventive approach can be recognized without evaluation of a Doppler effect.

In accordance with a preferred embodiment, a long range radar FMCW radar transmitter is used to generate partially overlapping or adjacent radar beams. The backscattered radar signals can each be assigned to a radiation cone. Called FMCW radar (engl. F requency M odulated C ontinuous W ave), also modulated continuous wave radar, a radar signal with constantly changing frequency. The frequency either increases linearly to drop abruptly to the initial value at a certain frequency (sawtooth pattern), or it can alternately rise and fall at a constant rate of change. By such a linear change of the frequency and a simultaneous continuous transmission, it is possible to determine apart from the differential speed between the transmitter and the object at the same time their absolute distance from each other.

A device according to the invention performs all the steps of the method according to the invention.

The computer program with program code means according to the invention is designed to perform all the steps of the method according to the invention when this computer program is carried out on a computer or a corresponding computing unit, in particular a device according to the invention.

The computer program product according to the invention with program code means, which are stored on a computer-readable data carrier, is provided for carrying out the method according to the invention when this computer program is carried out on a computer or a corresponding computing unit, in particular a device according to the invention.

The present invention is based on the recognition that radar sensors are degraded differently by the occurrence of precipitation in the signal transmission medium, depending on the operating frequency. The precipitation can be, for example, rain or snowfall. The effect of degradation occurs especially at higher frequencies, such as those used in automotive radar sensors and may cause different Degrationsgrade the radar signal depending on the precipitation intensity. Long Range Radar uses more than two radiation beams or antenna beams to locate objects in a traffic scenario. Provided receivers or sensors will receive the same intensity 1 in road traffic only if the radiated radar signal is backscattered by a radar cell homogeneously or uniformly filling object, such as rain. The radar cell corresponds to the field of view or fietd-of-view of the radar.

The approach of the invention can be used for a variety of applications. In the first place, the present invention enables detection of precipitation occurrence in the radar signal transmission medium. Furthermore, an intensity of the precipitate can be determined and a radar transmitter performance loss can be estimated. In order to maintain limited functionality of the radar transmitter in bad weather conditions, the present invention can be used to switch the system, e.g. a modulation system to which the current signal transmission medium is used. That is, it is conceivable, for example, to vary the power of the transmitted signals as a function of a determined precipitation. A further advantage of the approach according to the invention is that the method according to the invention can be applied in part without modification to existing automotive radar transmitters which produce at least two radiation cones. Future radar transmitters or systems may be optimized to take advantage of the benefits of the present invention. In addition, the approach according to the invention is suitable as a signal source for safety-relevant systems in vehicles.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically by means of embodiments in the drawings and will be described in detail below with reference to the drawings.

Brief description of the drawings

• FIG. 1 shows a schematic representation of a use of a radar system in traffic, according to an embodiment of the present invention;
• FIG. 2 shows a schematic representation of a homogeneous medium in a radar detected area according to an embodiment of the present invention;
• FIG. 3 shows a radar signal spectrum according to an embodiment of the present invention;
• FIG. 4 shows a flowchart of a preferred embodiment of the method according to the invention; and
• FIG. 5 shows a block diagram of a preferred embodiment of the device according to the invention.

Embodiments of the invention

Fig.1 shows an application of a multi-beam automotive radar system in traffic. A vehicle 1, also called a radar vehicle, is equipped with a long range radar system (LRR). The radar system includes at least one transmitter, at least one receiver, and processing means, such as a microprocessor for evaluating returned radiation received by the receiver. Transmitter and receiver are expediently implemented as an antenna, transmitting and receiving functions.

The vehicle 1 moves on a road which may be delimited by boundaries, for example in the form of a guard rail. On the road move further vehicles 3, which can be detected by the radar of the vehicle 1. For detecting the vehicles 3, the radar of the vehicle 1 emits a plurality of radar cones or antenna beams 4. An area detected by the antenna beams 4 is interspersed with precipitation, in this case Rain 5.

The main direction of movement of the precipitate is orthogonal to the radar beams. In the in Fig. 1 In the embodiment shown, the radar beams are emitted in the horizontal direction. The rain falls in a vertical direction.

Fig. 2 shows a schematic representation of raindrops in a monostatic radar cell. The radar cell may be an area that is one of those in Fig. 1 shown radiation cone 4 is detected. The monostatic radar cell is based on a radar located at the pointed end of the radiation cone. The angles θ and Φ indicate a horizontal or vertical antenna opening angle. The radar cell can be divided into two sections. A first section V ₁ starts from the radar and is limited by the radius R _min . The second section V _RZ adjoins the first section, has a length of d _R and is thus bounded by the radius R _min + d _R. The second section V _{RZ of} the radar cell is interspersed with rain 5 and thus represents a rain cell. Within the rain cell, apart from precipitation in the form of rain 5, there are no inhomogeneous objects, such as vehicles 3.

In the measurement with the long-range radar, a radar wave is emitted by a transmitter located on the vehicle 1, reflected on the object, for example a vehicle 3, and picked up again by a receiver assigned to the transmitter. The transit times and Doppler shifts that occur are used in radar sensors to determine the distance and relative speed of the object. In the long range radar, depending on the requirements of the radar visibility, several radiation cones 4 are used to localize objects to be detected in the traffic scenario. In this case, an object, for example for an FMCW radar system, results in a peak in the spectrum, which is detected simultaneously by two neighboring radiation cones. By analyzing the amplitude and phase ratio of these neighboring cone in the so-called "monopulse method", the angle to the object can be determined.

Figure 3 shows a signal spectrum using the example of the FMCW radar. The frequency f is plotted on the horizontal axis and the amplitude spectrum A of a backscattered signal (echo) on the vertical axis.

A first spectrum 31 shows an application in which a radar signal is reflected by a fixed object. The object may be, for example, one of the in Fig. 1 shown vehicles 3 act. The radar signal is not attenuated by precipitation. The first spectrum 31 therefore has a low noise floor 32 and a high peak. The peak, in the form of a peak shape, which clearly protrudes from the noise floor 32, will be caused by reflection of the radar signal on the object.

A second spectrum 34 shows an application in which the radar signal in turn is reflected by the object. In addition, the radar signal is damped by precipitation. The second spectrum 34 therefore has a high background noise 35. The noise floor 35 is significantly higher than that of the first spectrum 31. Further, the second spectrum 34 has a lower peak than the first spectrum 31. The increase of the background noise by precipitation is indicated by the reference numeral 37 and an object peak reduction by the reference numeral 38.

Signals reflected by a substance uniformly filling the radar cell, such as precipitate, will not give a peak in the spectrum of the FMCW radar. Instead, results in a broad frequency range distributed signal power, which significantly raises the noise floor 35 of the second spectrum 34. This signal power is used by all who, for example, in Fig. 1 reflected radiation cone 4 back and can be calculated for an object-free section of the radar cell from the measured spectral power density. This is done, for example, according to the principle of multiple scattering of the first order of narrow radiation cones (narrow-beam first order multiple scattering).

The location of in Fig. 2 shown, object-free area V _RZ of length d _R is in Fig. 3 is characterized as the spectral range located between the frequencies f _{R min} and f _{R min} + d _R. The region bounded by the frequencies f _{R_min} and f _{R min} + d _R therefore indicates an average rain backscatter from the rain cell 5. The average power backscattered by the rain is calculated by integrating the spectral power density measured with LRR in the section f _{R min} + d _R to f _{R min} + d _R + f _{dR of} the radar cell according to the multiple scattering principle mentioned. From this, the rain intensity can be determined via the backscatter cross section of the rain and thus the radar signal attenuation or the LRR performance loss.

Fig. 4 FIG. 12 shows a flowchart of a method for detecting precipitation in a radar-detected area according to a preferred embodiment of the present invention. In a first step 401, at least two radiation capsules which are not or only partially overlap are emitted by means of at least one corresponding transmitter (antenna). In a further step 402, a first average power of a first backscattered radar signal is determined. In a further step 404, a second average power of a second backscattered radar signal is determined. In a third step 406, a determination and optionally an indication of the presence of precipitation takes place with a correspondence of the average powers of the two backscattered signals.

In the area covered by the radiation cones or radar beams, for example, the area covered in FIG Fig. 1 act shown area which is covered by the radiation cone 4. The precipitate may be inhomogeneity of the area detected by radar beams, except for existing solid objects which are inhomogeneity with respect to the detected area, for example in the form of in Fig.1 shown vehicles 3, evenly. In contrast to fixed objects, which are impermeable to radar beams, radar beams can partially penetrate the precipitation.

As in Fig.1 shown, can be used in the implementation of the method according to the invention multiple beam cone 4. In the in Fig. 1 shown embodiment, four beam cones are used. Accordingly, for the inventive method further backscattered radar signals for detecting Precipitation be used. In this case, the method according to the invention can have one or more further steps of determining one or more further average powers. The other average powers are determined from the further backscattered radar signals. The backscattered radar signals may be generated by reflection from radar signals emitted by adjacent radar transmitters (antennas). In Fig.1 For example, the radar signals are emitted by radar transmitters or antennas which are arranged adjacent to a front side of the vehicle 1. It is also conceivable to cover the entire area covered by the radiation cone 4 by means of a single antenna, which is embodied correspondingly pivotable between the transmission of individual radiation cones.

If all the radiation cones 4 used to generate the backscattered radar signals have the same antenna characteristics, the associated radar sensors or receivers will detect the same backscattered mean intensity I as follows: $${\mathrm{I}}_{\mathrm{b}\mathrm{1}}\mathrm{=}{\mathrm{I}}_{\mathrm{b}\mathrm{2}}\mathrm{=}{\mathrm{I}}_{\mathrm{b}\mathrm{3}}\mathrm{=}{\mathrm{I}}_{\mathrm{b}\mathrm{4}}\mathrm{=}\mathrm{...}\mathrm{=}{\mathrm{I}}_{\mathrm{bn}}$$

I _bi (i = 1-n) stands for the average intensity of a backscattered radar signal of the i-th radiation cone.

If the radiation cones have different antenna characteristics, then the average powers can be adapted to each other. A determination of the correspondence of the mean powers I can then take place taking into account at least one weighting factor, wherein the at least one weighting factor is designed to compensate for different radar antenna characteristics.

According to this embodiment, the average intensity can be calculated taking into account the different antenna characteristics as follows: $${\mathrm{\alpha }}_{\mathrm{b}\mathrm{1}}{\mathrm{I}}_{\mathrm{b}\mathrm{1}}\mathrm{=}{\mathrm{\alpha }}_{\mathrm{b}\mathrm{2}}{\mathrm{I}}_{\mathrm{b}\mathrm{2}}\mathrm{=}{\mathrm{\alpha }}_{\mathrm{b}\mathrm{3}}{\mathrm{I}}_{\mathrm{b}\mathrm{3}}\mathrm{=}{\mathrm{\alpha }}_{\mathrm{b}\mathrm{4}}{\mathrm{I}}_{\mathrm{b}\mathrm{4}}\mathrm{=}\mathrm{...}\mathrm{=}{\mathrm{\alpha }}_{\mathrm{bn}}{\mathrm{I}}_{\mathrm{bn}}$$

Here, α _bi (i = In) represent the weighting factors or Leistungsverhälmisse between a radiation cone i and a reference selected radiation cone, eg the radiation cone with the maximum power. This approach can be used for the automatic detection of precipitation when using all radar types.

According to this embodiment, the average powers are each determined for an object-free portion of the detected area. To this end, the steps of determining may each comprise a step of detecting a spectral power density of the backscattered radar signal and a step of integrating the spectral power density, respectively over the non-object portion. Related to Fig. 3 this means that, for example, an integration of the second characteristic curve 34 takes place via the section f _{R min} , f _{R min + dR} .

The non-object portion can be determined by analyzing the spectral power densities of the backscattered radar signals. In this case, the object-free section corresponds to a common subarea of the spectral power densities in which none of the spectral power densities has a peak. Such a peak is characterized in that it stands out clearly over a noise of the respective spectral power density and thus indicates a fixed, with respect to its homogeneous environment inhomogeneous object. Such an outstanding peak is in Fig. 3 shown.

According to the illustrated embodiment, a match of the average powers can be determined by means of a correlation of the mean powers. If the correlation result indicates a match of the mean powers, then a homogeneous distributed medium such as precipitation was recognized. This can be indicated by a signal, for example.

As in Fig. 3 As shown, precipitation in the area covered by radar beams causes an increase in the noise floor. By evaluating the increase in at least one of the spectral power densities, a density of the homogeneously distributed medium, that is, for example, a rain intensity, can be determined by means of a radar signal attenuation. The increase can be done, for example, by comparing a current noise floor with a stored Referenzgrundrauschens. The Radar signal attenuation indicates how much a radar signal is attenuated by the precipitate. Values indicating the density of the homogeneously distributed medium as well as the radar signal attenuation can also be displayed by means of signals.

Fig. 5 shows an apparatus for detecting precipitation in a radar detected area, according to an embodiment of the present invention. The apparatus is configured to receive a first backscattered radar signal 501 and a second backscattered radar signal 502 and to provide a detection signal 503 indicative of the presence of a homogeneously distributed medium, such as precipitation. For this purpose, the device has two transmitters 550, 552 for transmitting radar radiation or radar signals 560, 562 and two receivers 512, 513 for receiving the backscattered radar signals 501, 502. The receivers 512, 513 are configured to provide the spectra of the backscattered radar signals 501, 502 to detectors 514, 516. The decomposers 514, 516 are designed to calculate the average signal powers from the spectra and to provide them to a comparator 518. The comparison device 518, for example in the form of a correlator, is designed to compare the mean signal powers with one another. If the signal powers agree, it is assumed that a homogeneously distributed medium is located in the area covered by the radar beams. To determine a match, a predetermined tolerance range can be used. The tolerance range can be based on the height of the noise floor.

In order to determine the object-free region, the device may comprise an analyzer 522, which is designed to determine the object-free region from the spectra provided by the receivers 512, 513 and to provide them to the investigators 514, 516.

According to the approach of the invention, the radar signal is orthogonal to the precipitate. Therefore, no Doppler evaluation is possible, but there is a determination of the rain intensity on the reflectivity and by integration of rain backscatter or the Rauschflooranhebung in the vicinity, for example, an FMC W radar system.

The rain detection in the traffic is done by the correlation of the average power from several neighboring antenna arrays. The radar system used may be, for example, a 76.4 GHz automotive radar system that is not stationary due to an arrangement on a vehicle, for example.

Claims (12)

1. Method for identification of precipitation (5) in an area which is covered by radar beams (4), with the method being characterized by the following steps:

   transmission (401) of at least two radar signals with radiation lobes which do not overlap, or overlap only partially;

   determination (402) of a first mean power of a first back-scattered radar signal (501);

   determination (404) of a second mean power of a second back-scattered radar signal (502);

   detection (406) of the presence of precipitation by comparison of the determined mean powers with one another,

   characterized in that the mean powers are compared taking account of at least one weighting factor, with the at least one weighting factor being designed to compensate for different radar antenna characteristics.
2. Method according to Claim 1, characterized by a further step of determination of a further mean power of a further back-scattered radar signal, in which case the back-scattered radar signals can be produced by reflection of radar signals (4; 560, 562) which are transmitted by radar antennas and transmitters (550, 552) which are arranged adjacent.
3. Method according to one of the preceding claims, characterized in that the mean powers are each determined for a section (V_RZ) of the covered area in which there are no objects.
4. Method according to Claim 3, characterized in that the determination steps have the following steps:

   detection of in each case one power spectral density for each back-scattered radar signal (501, 502);

   integration of the power spectral densities (31, 34), in each case over the section (V_RZ) in which there are no objects, in order to obtain the mean powers.
5. Method according to Claim 4, characterized in that the section in which there are no objects is determined by analysis of the power spectral densities (31, 34) of the back-scattered radar signals (501, 502), with the section (V_RZ) in which there are no objects corresponding to a common subarea of the power spectral densities in which none of the power spectral densities have a peak which projects above the background noise (32, 35) of the respective power spectral densities.
6. Method according to one of the preceding claims, characterized in that the comparison of the mean powers comprises detection of a match between the mean powers, in particular by means of correlation.
7. Method according to one of Claims 4 to 6, with the method furthermore being characterized by a step of evaluation of a peak (37) in the background noise of at least one of the power spectral densities (31, 34), in order to determine a density of precipitation (5) or radar signal attenuation.
8. Method according to one of the preceding claims, characterized in that the precipitation is rain, hail or snowfall, whose main moving direction is at right angles to the radar beams (4).
9. Method according to one of the preceding claims, characterized in that a long-range radar FMCW radar transmitter is used, in order to produce radiation lobes which partially overlap one another or are located alongside one another, in which case the back-scattered radar signals can each be associated with one radiation lobe.
10. Apparatus for carrying out all the steps of a method according to one of Claims 1 to 9.
11. Computer program having program code means for carrying out all the steps of a method according to one of Claims 1 to 9 when the computer program is run on a computer or a corresponding computer unit.
12. Computer program product having program code means which are stored in a computer-legible data storage medium, in order to carry out all the steps of a method according to one of Claims 1 to 9 when the computer program product is run on a computer or a corresponding computer unit.

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